The version of SharePoint that comes with SBS 2008 works best with SBS 2008. You can install SharePoint 2010 Foundation on SBS 2008 but it means uninstalling the old version and disabling all the wizards.

The other issue is that SharePoint v3 has an unlimited database size whereas the best you can get with SharePoint Foundation 2010 would be 10GB, which you'll find customers fill very fast.

My gut tells me that install SharePoint Foundation 2010 on SBS 2008, although supported, will result in issues down the track when it comes to patches and the like.

I had the same problem. The solution is: 1) back-up content databases, 2) uninstall sharepoint (WSS), 3) install SQL Server 2008 or you can you SQL server on a different box (I installed R2 Express edition), 4) install sharepoint foundation 2010 (WFE only mode, not stand-alone), 5) after installation mount content databases. It worked for me.

The version of SharePoint that comes with SBS 2008 works best with SBS 2008. You can install SharePoint 2010 Foundation on SBS 2008 but it means uninstalling the old version and disabling all the wizards.

The other issue is that SharePoint v3 has an unlimited database size whereas the best you can get with SharePoint Foundation 2010 would be 10GB, which you'll find customers fill very fast.

My gut tells me that install SharePoint Foundation 2010 on SBS 2008, although supported, will result in issues down the track when it comes to patches and the like.